Polyisocyanates have been reacted in the presence of a trimerization catalyst to produce polyisocyanurate foams, in an attempt to produce foams which produce a high char resistance to fire and of low smoke values. The trimerization of polyisocyanurate produces foams of superior fire performance over conventional polyurethane foams. In order to correct or mask certain undesirable properties in polyisocyanurate foams, it has been the practice to incorporate small amounts of urethane polyols in the isocyanate reaction mixture, to produce a modified urethane polyisocyanurate foam. However, the addition of such polyols often leads to degradation of the fire and smoke properties of the modified foam composition.
Polyurethane coating compositions have been prepared employing elastomeric urethanes made by reacting polyethers with toluene diisocyanate or polymeric low-functionality methylene diisocyanates. Often, these elastomeric urethanes are employed in injection-molding processes. The elastomeric coating is controlled in flexibility usually by the option of employing a higher-molecular-weight triol, with the reaction usually carried out in the presence of various types of tin catalysts. The elastomeric urethane coatings so produced are not wholly satisfactory, in that they tend to burn and melt when exposed to flame. The tensile strength of such urethane elastomeric coatings are often increased by adding various diols to the polyether triol compositions, with 1,4 butane diol being an industry standard used in increasing flexibility and tensile strength.
In the parent application, an isocyanurate thermosetting foam composition is described having improved flame, smoke and nonburning properties with high char resistance. The rigid-foam composition so prepared is suitable for use in the contruction and insulation fields, such as, for example, in forming rigid insulation panels or foam-board stock. Typically, the rigid foam composition is prepared by the reaction of 100 parts of a methylene diisocyanate having a low functionality, with or without the presence of melamine, and with a methoxy polyethylene glycol and, optionally, with a diethylene glycol, a surfactant, a trimerization catalyst and a blowing agent, typically to provide a closed-cell, thermosetting, modified isocyanurate foam having a low flame-spread value.